#include <bits/stdc++.h>
using namespace std;

class Solution
{
public:
    int missingNumber(vector<int> &nums)
    {
        int ret = 0;
        for (auto &ch : nums)
            ret ^= ch;
        for (int i = 0; i <= nums.size(); i++)
        {
            ret ^= i;
        }
        return ret;
    }
};
int main()
{
    return 0;
}
